Powell, a 20-year-old professional wake boarder, returned to the U.S. while his girlfriend stayed back in Australia to work at her family's zoo. It was an emotional farewell for the couple, who shared goodbye messages on Instagram.

"You are flying back to the U.S.A. today. Dropping you off at the airport and waving goodbye, it never gets easier. Thank you for the most wonderful adventures these last few months," Irwin captioned a photo of herself resting her head on Powell's shoulder. "I've known you since you were 16 and every day, from the very first day I met you, you've been my sunshine."

"I will see you again soon!" the 18-year-old conservationist continued. "Thank you for everything, you always make me smile, no matter how far apart we may be. Have fun while you're away, go find lots of manatees in Florida for me! I miss you so much already. You really do mean the world to me."

Powell also expressed how hard it was to leave Irwin in Australia. "It seems like just yesterday I arrived in Australia for your birthday. Each goodbye gets more and more difficult," he posted, along with a photo taken by Irwin's brother Robert. "I always carry even the smallest of moments, like these sunset walks through the zoo, with me no matter where I go. Counting down the days until I'm back with you again creating more incredible, unforgettable memories. Thank you for making me so happy each and every day."

Every chance they get, these two can't help but gush over one another. In their first joint interview in October, Irwin shared exclusively with ET the "defining moment" when she first realized Powell was the one for her. Check it out: